Ferrite Films Research Articles

Influence of film thickness on microstructure and optical properties of Bismuth Ferrite (BFO) for photovoltaic application

Bismuth Ferrite (BFO) film with a low bandgap value is a promising candidate for photovoltaic applications. This study discussed the effects of film thickness on the microstructure and optical properties of BFO films. BFO films were deposited on the Quartz-Silicon substrates using the chemical solution deposition (CSD) method. The thickness variation was conducted by varying the deposited layer number which correspond to the thickness values of 252 and 405 nm, respectively. The XRD analysis showed that increasing of films thickness had no significant effect on the crystal structure. It revealed that the XRD peak intensities increase, however, the lattice parameters, crystallite size, and crystallinity are relatively in the close values as the increasing films thickness. The Scanning Electron Microscopy (SEM) analysis exhibited the larger grain size of the BFO films with the increasing films thickness. According to the UV-Vis spectrophotometer results, the bandgap values reduced from 2.48 eV to 2.5 eV as the thicker film. Finally, The I-V curve presented that the higher films thickness induced the higher efficiency of the BFO film from 0.97 % to 2.1%. The BFO film with higher thickness could exhibit the better performance for photovoltaic application.

Magnetoelastic constant of thin films determined by a four-point bending apparatus

We have developed a method to variably induce lattice strains and to quantitatively evaluate the induced magnetic anisotropy. Both tensile and compressive strains were introduced into epitaxial films of cobalt ferrite (CFO) grown on a single crystal MgO(001) substrate using a four-point bending apparatus made of a plastic material fabricated by a 3D printer. The change in magnetic anisotropy due to bending strain can be measured quantitatively by using the conventional magneto-torque meter. The strain-induced magnetic anisotropy increased with the tensile strain and decreased with the compressive strain as expected from a phenomenological magnetoelastic theory. The magnetoelastic constant obtained from the changes in bending strains shows quantitatively good agreement with that of the CFO films with a uniaxial epitaxial strain. This signifies that the magnetoelastic constant can be evaluated by measuring only one film sample with strains applied by using the bending apparatus.

Growth and characterization of ultrathin cobalt ferrite films on Pt(111)

CoFe2O4 thin films (5 nm and 20 nm thick) were grown by oxygen assisted molecular beam epitaxy on Pt(111) at 523 K and subsequently annealed at 773 K in vacuum or oxygen. They were characterized in-situ using Auger Electron Spectroscopy, Low-Energy Electron Diffraction, Scanning Tunneling Microscopy and Conversion Electron Mössbauer Spectroscopy. The as-grown films were composed of small, nanometric grains. Annealing of the films produced an increase in the grain size and gave rise to magnetic order at room temperature, although with a fraction of the films remaining in the paramagnetic state. Annealing also induced cobalt segregation to the surface of the thicker films. The measured Mössbauer spectra at low temperature were indicative of cobalt ferrite, the both films showing very similar hyperfine patterns. Annealing in oxygen or vacuum affected the cationic distribution, which was closer to that expected for an inverse spinel in the case of annealing in an oxygen atmosphere.

Decoupling Technique Using Ferrite-Film Loading for 5G MIMO Applications

Decreasing the mutual coupling between multiple-input-multiple-output (MIMO) antenna elements requires the selection of an appropriate decoupling technique without changing the geometry or operating frequency of the antenna. In this paper, a simple and flexible approach that involves loading a small ferrite film on the radiation patch of an MIMO antenna pair has been proposed to mitigate the unwanted mutual coupling. Through a thorough investigation, the two IFA elements with an element distance of only 1.4 mm can be decoupled adequately by properly controlling the ferrite-film loading area and the thickness of the ferrite film, along with maintaining the desired operating frequencies and acceptable radiation characteristics at the LTE Band 42 (3.4–3.6 GHz). The optimum ferrite-film loading on the grounding branch of the IFA element can increase the isolation from −6.64 dB to −10.43 dB and enhance the bandwidth from 3.20–3.88 GHz to 2.83–3.65 GHz, and its efficiency can reach to 45.5%, as well as a 2 dB gain. A physical model has also been established to interpret the operating mechanism of ferrite-film loading on the IFAs. The proposed simulated procedure is validated via measurements. This technique of ferrite loading on MIMO antennas can effectively decouple the mutual coupling at a low cost and with low design complexity, indicating its potential applicability for use in MIMO antennas in mobile handsets.

Dependence of the Threshold Field Intensity of Ferrite Films on Intrinsic Damping and Secondary Microwave Signal

Nonlinearity is important for a wide variety of engineering applications. Magnon scattering processes can be exploited in order to realize energy-efficient magnonic devices. The ability of an additional secondary microwave signal in modifying such nonlinear behavior becomes important in the context of dynamic control of nonlinearity. However, an application-oriented study of the nonlinearity dependence on various parameters remains to be carried out. In this work, we demonstrate the dependence of threshold field intensity on intrinsic damping and the field intensity of the secondary signal. The secondary frequency at which the threshold attains the maxima is shown to scale with the intrinsic damping. In addition, the increase in the intensity of the secondary frequency is found to increase the primary threshold field, thus allowing for dynamic control of nonlinearity. We also explain the position of cusps that occur in the threshold field intensity as the secondary signal frequency is varied.

Tunning the Physical Properties of PVDF/PVC/Zinc Ferrite Nanocomposites Films for More Efficient Adsorption of Cd (II)

This work deals with the synthesis of ZnFe2O4 NPs and studies the effect of addition on the physical properties PVDF/PVC blend. XRD affirmed the formation of ZnFe2O4 NPs and HRTEM shows that the size of the prepared ZnFe2O4 NPs ranged from 20 to 55 nm. The effect of ZnFe2O4 on the behavior of PVDF/PVC was studied through XRD, ATR-FTIR, FESEM and UV–Visible spectroscopy. XRD revealed that the addition of ZnFe2O4 NPs enhanced the crystallinity of PVDF/PVC blend system and also confirmed the incorporation of ZnFe2O4 NPs by appearing a diffraction peak at 2θ equals 35°. ATR-FTIR affirmed the interaction between blend sample and ZnFe2O4 NPs by appearing new bands 554 cm−1 and 421 cm−1 which are corresponded to ZnFe2O4 NPs functional group with appearing a new band at 603 cm−1. FESEM showed that the addition of ZnFe2O4 to PVDF/PVC blend improved surface properties, for example, roughness average has been increased from 319 to 414 nm while maximum height increased from 260 to 473 nm for PVDF/PVC and PVDF/PVC/10% ZnFe2O4, respectively. Optical properties and band gap calculations revealed that addition of ZnFe2O4 NPs changes the structure of polyblend samples which results due to the formation of localized states. The removal efficiency of Cd (II) by using PVDF/PVC/10% ZnFe2O4 reached about 50% at pH 6 after 60 min. the absorption mechanism as well as kinetics isotherm have been studied. It is found that adsorption of Cd (II) occurred through the Langmuir mechanism and fellow pseudo-second order isotherm.

Small magnetless integrated optical isolator using a magnetized cobalt ferrite film

We experimentally demonstrated a silicon optical isolator using a monolithically integrated cobalt ferrite (CFO) film as magneto-optical material, achieving an isolation ratio of 9.6dB near 1550nm wavelength. By virtue of the large Faraday rotation coefficient of CFO, the device has a compact footprint comparing to the current yttrium iron garnet-based isolators. Furthermore, we demonstrated self-biased isolation by the strong remanence of CFO films, eliminating the tedious demand of an external magnet. Cobalt ferrite represents a potential alternative approach to yttrium iron garnets to realize a practical device for on-chip isolation in silicon photonic integrated circuits because of the small footprint.

Greatly enhanced photocurrent density in bismuth ferrite films by Localized Surface Plasmon Resonance effect

Very recently, the ferroelectric photovoltaic effect of multiferroic BiFeO3 (BFO) has attracted much attention because of its large photovoltage beyond the bandgap and unique photocurrent switchable characteristics. However, the poor short-circuit current density (JSC ∼ μA/cm2) of BFO leads to a low power conversion efficiency (PCE), which greatly hinders its application and development as photovoltaic or optoelectronic devices. In this paper, a novel heterostructure comprised Au nanoparticles layer and BiFe0.9375Mn0.0625O3 (BFMO) thin film was constructed. The results and analysis showed that the photocurrent densities of all these heterostructures were greatly improved in comparison with that of pure BFMO film without Au layer. Especially, the maximum photocurrent density of 1.323 mA/cm2 was observed in the heterostructure of BFMO-Au-1 m, which is 50 times higher than that of pure BFMO film (26 μA/cm2). A possible mechanism was herein proposed that the Localized Surface Plasmon Resonance (LSPR) effect derived from Au nanoparticles might play a key role on the enhanced photocurrent densities of these heterostructures. Firstly, LSPR effect would effectively amplify the intensity of the incident light partially passing through BFMO film and then reentering the film through the diffuse reflection, which greatly enhance the light absorption of the film. Secondly, the locally strengthened electric field around Au nanoparticles greatly enhances the migration rate of surrounding electrons, and thus improves the separation efficiency of electron-hole pairs. Consequently, the photocurrent density of BFMO film was greatly enhanced by LSPR effect.

Twofold and fourfold anisotropies in zinc ferrite thin films investigated by ferromagnetic resonance

By means of the ferromagnetic resonance (FMR) technique (at the $X$ band) we investigated the magnetic properties of ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$ (ZFO) films grown on different substrates. Angular dependence of the FMR field showed the existence of twofold and fourfold anisotropies for the same material, grown on Si(111), MgO(100), and STO(100), respectively. By using a model that takes into consideration the relevant contributions to the energy, we were able to extract the following parameters: effective magnetization ${M}_{\mathrm{eff}}$, cubic magnetocrystalline anisotropy field, in-plane and out of plane uniaxial anisotropy fields, and the $g$ factor. The samples deposited on Si showed a twofold in-plane anisotropy while a fourfold magnetic anisotropy was observed for the ZFO/MgO and ZFO/${\mathrm{SrTiO}}_{3}$ samples. All samples showed a strong perpendicular uniaxial anisotropy above 1 kOe and low in-plane uniaxial and cubic anisotropy field, on the order of tens of oersteds. The FMR linewidth ($\mathrm{\ensuremath{\Delta}}H$) fitted from FMR data shows $\mathrm{\ensuremath{\Delta}}H$ values above 190 Oe for all samples, indicating high damping of this material to be $\ensuremath{\sim}{10}^{\ensuremath{-}2}$ for the ZFO/MgO. The present analysis compared the FMR data obtained for the in-plane and out of plane measurements. Likewise, the effective magnetization and perpendicular uniaxial anisotropy field by FMR were compared with the magnetic response obtained by a vibrating sample magnetometer.

Electrical and optical properties of thin-film bismuth ferrite

The optical and electrical properties of bismuth ferrite thin films obtained by high-frequency magnetron sputtering in an atmosphere of argon and oxygen (80%+20%) has been studied. Investigations of the optical properties have shown that for polycrystalline bismuth ferrite films the optical band gap is ~2.3 eV, which is in the range of given in the literature values. The dependences of the specific electrical conductivity on the magnitude of the electric field has been studied for the synthesized films. It has been established that the electrical conductivity does not depend on the electric field strength up to the value of E=2.1·106 V/m. The experimental results are discussed in terms of the model of charge carrier injection from aluminum electrode into the conduction band of bismuth ferrite. Keywords: electrical conductivity, strong electric fields, optical absorption coefficient, memristor effect.

Электрические и оптические свойства тонкопленочного феррита висмута

The optical and electrical properties of bismuth ferrite thin films obtained by high-frequency magnetron sputtering in an atmosphere of argon and oxygen (80% + 20%) has been studied. Investigations of the optical properties have shown that for polycrystalline bismuth ferrite films the optical band gap is ~3 eV, which is in the range of given in the literature values. The dependences of the specific electrical conductivity on the magnitude of the electric field has been studied for the synthesized films. It has been established that the electrical conductivity does not depend on the electric field strength up to the value of E = 2.1106 V/m. The experimental results are discussed in terms of the model of charge carrier injection from aluminum electrode into the conduction band of bismuth ferrite.

Influence of sintering temperature on structural, morphological and optical properties of nanocrystalline bismuth ferrite thin films via sol-gel processing

Nanocrystalline thin films of pure bismuth ferrite were synthesized by sol-gel deposition technique on the corning glass substrate. The influence of sintering temperature on microstructure, morphology, and optical parameters has been systematicallystudied. Optimization of sintering temperature for single-phase nanocrystalline bismuth ferrite fabrication was carried out and found to be at 550 °C. X-ray diffraction confirms the presenceof distortedrhombohedral perovskite structure of bismuth ferrite oriented along (hkl) plane of (101).Surface morphology and Root mean square (RMS) surface roughness of the thin films prepared were determined from the micrographs of atomic force microscopy (AFM).Several optical constants viz. bandgap energy, extinction coefficient,Urbach energy, has been determined using Ultraviolet-Visible spectroscopy of the thin films within the range 200 -800 nm. With the increase in sintering temperature, there is a decrease in the optical bandgap of the material which would be essential for the wide range of applications in thin-film solar cells along with optoelectronic devices.

Preparation, structural features, elemental composition of and dielectric properties of a two-layer structure based on thin films of multiferroic BiFeO-=SUB=-3-=/SUB=- and ferroelectric (Sr, Ba)Nb-=SUB=-2-=/SUB=-O-=SUB=-6-=/SUB=-

BiFeO heterostructures were manufactured using intermittent sputtering technology on the surface of a single crystal substrate MgO(001) BiFeO3/(Sr, Ba)Nb2O6. Studies of the structure, thickness profile of the composition, surface morphology and dielectric characteristics of materials have been carried out. It is established that despite the formation of two types of orientation domains (±18.4o) in the layer (Sr, Ba)Nb2O6, the upper layer of BiFeO3 is in the ratio of the total parallel orientation with the substrate MgO(001). It is shown that the composition of the films of bismuth ferrite and barium-strontium niobate does not change in film thickness, corresponds to the compositions of the sprayed ceramic targets, no signs of the presence of buffer layers were revealed. The results of the study of dielectric and ferroelectric characteristics of the heterostructure are presented. The reasons for the revealed patterns are discussed. Keywords: thin films, heterostructure, barium-strontium niobate, bismuth ferrite.

Performance modulation through selective, homogenous surface doping of lanthanum strontium ferrite electrodes revealed by in situ PLD impedance measurements.

Accelerating the oxygen reduction kinetics of solid oxide fuel cell (SOFC) cathodes is crucial to improve their efficiency and thus to provide the basis for an economically feasible application of intermediate temperature SOFCs. In this work, minor amounts of Pt were doped into lanthanum strontium ferrite (LSF) thin film electrodes to modulate the material's oxygen exchange performance. Surprisingly, Pt was found to be incorporated on the B-site of the perovskite electrode as non metallic Pt4+. The polarization resistance of LSF thin film electrodes with and without additional Pt surface doping was compared directly after film growth employing in situ electrochemical impedance spectroscopy inside a PLD chamber (i-PLD). This technique enables observation of the polarization resistance of pristine electrodes unaltered by degradation or any external contamination of the electrode surface. Moreover, growth of multi-layers of materials with different compositions on the very same single crystalline electrolyte substrate combined with in situ impedance measurements allow excellent comparability of different materials. Even a 5 nm layer of Pt doped LSF (1.5 at% Pt), i.e. a Pt loading of 80 ng cm−2, improved the polarization resistance by a factor of about 2.5. In addition, p(O2) and temperature dependent impedance measurements on both pure and Pt doped LSF were performed in situ and obtained similar activation energies and p(O2) dependence of the polarization resistance, which allow us to make far reaching mechanistic conclusions indicating that Pt4+ introduces additional active sites.

Optical properties of bismuth ferrite multiferroic films determined by spectroscopic ellipsometry

Optical properties of bismuth ferrite multiferroic films determined by spectroscopic ellipsometry

Plug and Play Electrodeposition Cell: A Case Study of Bismuth Ferrite Thin Films for Photoelectrochemical Water Splitting

In the present study, we designed and fabricated a cost-effective miniaturized versatile electrochemical deposition cell, which is found to be at par performance as compared with conventional electrodeposition techniques. A case study is being undertaken for the electrodeposition of varied thicknesses of bismuth ferrite (BiFeO3) films on FTO glass substrates. X-ray diffraction (XRD) patterns confirm the structural perovskite phase of BiFeO3 (BFO). UV–visible absorption spectra and Tauc plot of BFO estimate the direct band gap which lies between 1.9 to 2.1 eV. The properties of the bismuth ferrite crystal system such as electronic band structure and density of states (DOS) are investigated theoretically. Photoelectrochemical (PEC) water splitting application is carried out to investigate the best performance of BFO films of varied thicknesses. The best performer (BFO15) working electrode yields a photocurrent density of ∼35 μA cm−2 at 0.2 V vs RHE under visible LED (light intensity of 100 mW cm−2) in neutral 0.5 M Na2SO4 electrolyte. Incident photon to current conversion (IPCE) measurements, electrochemical impedance spectroscopy (EIS), and Mott-Schottky characteristics confirm the best performance of BFO15 photocathode film.

Structural, optical, and dispersive parameters of (Gd, Mn) co-doped BiFeO3 thin film

Nanocrystalline bismuth ferrite thin films co-doped with Gd and Mn were successfully fabricated via sol-gel spin coating method onto the corning glass substrate. The effect of Gd and Mn incorporation at A and B sites of bismuth ferrite perovskite on its structural, microstructural, and optical properties was studied systematically. The starting material for the synthesis of the samples was bismuth nitrate, ferrite nitrate, gadolinium nitrate and manganese acetate. These precursors were dissolved in 2-methoxy ethanol to prepare the sol, which was spin-coated at an optimized rate of 3000 rpm for 30 s on corning glass substrate. The samples were heated subsequently at 350 °C for 5 min on a hot plate in the open air and further annealed at 550 °C for 2 h at a muffle furnace for crystallization of the as-prepared thin film. X-ray diffraction analysis reveals the existence of distorted rhombohedral perovskite structure with preferred orientations along the (101) plane. The incorporation of Gd and Mn in bismuth ferrite perovskite was confirmed from Raman spectra measured at room temperature. Surface morphology and microstructural studies were carried out using Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM). Several optical parameters like bandgap energy, Urbach energy, Extinction co-efficient, Near Edge Absorption ratio were determined from Ultraviolet–Visible spectra of the film prepared. The variation of refractive index, permittivity, loss tangent as a function of wavelength were plotted and discussed. Real and imaginary parts of dielectric functions as a function of wavelength were reported. The correlation between the structural and the microstructural parameters with the optical parameters was investigated in this work.

High Remanence Ratio of Aluminum Substituted Hexagonal Barium Ferrite Films for Self-Biased Microwave Devices

High Remanence Ratio of Aluminum Substituted Hexagonal Barium Ferrite Films for Self-Biased Microwave Devices

Mechanism of improving transverse corner cracks of peritectic steel slab based on control of inclusions and microstructures with magnesium treatment

In this paper, in order to clarify the mechanism of improving the transverse corner crack of peritectic steel slab with Mg treatment, the inclusions and microstructure characteristics at the slab corner of Al deoxidized (S-Al), (Al+Ca) deoxidized (S-Ca) and (Al+Mg) deoxidized (S-Mg) peritectic steels were studied. The inclusions in S-Al sample are mainly Al2O3, Al2O3 · MnS and MnS inclusions. The S-Ca sample mainly contains Al2O3 inclusions and their complex inclusions. In the S-Mg sample, the number of Mg containing inclusions increase sharply. The S-Mg sample has the smallest average size of inclusions and the largest number of inclusions with the size smaller than 1 µm. The brittle structures are dominant in S-Al sample, which basically disappear in S-Ca sample and S-Mg sample. Mg treatment refines the size of grains at the slab corner, reduces the size of the proeutectoid ferrite films, and restrains the crack propagation along the grain boundary. More IAF microstructures are formed in S-Mg sample. IAFs take MgO · Al2O3 · MnS, MgO · Al2O3 · TiN · MnS and other complex inclusions as the nucleation cores, which diverge and grow outward from the inclusions. Thus, IAFs form a fine crack resistant microstructure, improving the microstructure at the slab corner to prevent the occurrence of transverse corner cracks.

Cationic Ordering and Its Influence on the Magnetic Properties of Co-Rich Cobalt Ferrite Thin Films Prepared by Reactive Solid Phase Epitaxy on Nb-Doped SrTiO3(001).

Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich films with different stoichiometry ( and ) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/FeO bilayers deposited before on Nb-doped SrTiO(001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of cations in the low-spin state on octahedral sites for the film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements.